The present invention relates to a processing reactor and, more particularly to a processing reactor for the thermal processing and chemical deposition of thin film applications on a substrate, such as semiconductor wafer, in which the temperature of the substrate can be accurately monitored and the injection of gas into the chamber can be controlled to provide better control of the substrate processing.
In semiconductor fabrication, semiconductor substrates are heated during various temperature activated processes for example, during film deposition, oxide growth, etching, and thermal annealing. The control of deposition and annealing processes depends on the control of the gas flow and pressure and the wafer temperature. When heating a substrate, it is desirable to heat the substrate in a uniform manner so that all the regions of the substrate are heated to the same temperature. Uniform temperatures in the substrate provide uniform process variables on the substrate; for instance in film deposition, if the temperature in one region of the substrate varies from another region, the thickness of the deposition in these regions may not be equal. Moreover, the adhesion of the deposition to the substrate may vary as well. Furthermore, if the temperature in one region of the substrate is higher or lower than the temperature in another region of the substrate, a temperature gradient within the substrate material is formed. This temperature gradient produces thermal moments in the substrates which in turn induce radial local thermal stresses in the substrate. These local thermal stresses can reduce the substrate""s strength and, furthermore, damage the substrate. Therefore, knowing the temperature of the wafer is important in determining the thermal diffusion depths of surface implanted dopants, the deposited film thickness, and the material constitution quality and annealed or reflowed characteristics.
Various methods have been developed for measuring the temperature of a substrate during processing in order to improve the control of the various processes. Direct methods, which include the use of contact probes, such as thermocouples or resistance wire thermometers, are generally not suitable for substrate processing because direct contact between the probes and the substrate contaminates the device structure. More typically, indirect measuring methods are used, such as the use of preheated platforms that are calibrated prior to processing. However, this method is not typically accurate. In some applications, the temperature of the back side of the substrate is calibrated or monitored, but such methods also lead to significant errors due to the large variances between the back side and device side surface characteristics that lead to different substrate temperatures. The patterns of the specific devices being processed, the type of material being deposited or annealed, the degree of the roughness of the surface, and the operating temperature all affect the characteristics of the substrate surface and define what is known as the surface emissivity of the substrate.
In U.S. Pat. No. 5,310,260 to Schietinger et al. a non-contact temperature measuring device is disclosed. The device includes two sapphire optical fibre probes, with one of the probes directed to the lamp source providing the heat to the wafer and the other probe directed to the wafer itself. Each fiber probe sends its respective signal to a measuring instrument which converts the photon density measured by the probe to an electrical current. The ratio of the two signals provides a measure of the surface reflectivity, which approximates the total hemispherical reflectivity. However, this method can only be used with an AC source lamp and when the lamp shines directly on the wafer. Since two optical fiber probes must be used in order to implement this technique, the characteristics of each probe must be accurately detailed in order to obtain accurate emissivity measurements. In the event that one of the probes must be replaced, a total system re-calibration is required. Furthermore, this method cannot be used in chambers in which thin films are deposited, etched, or sputtered since the thin films will also deposit on the optical fiber photon density sensors and drastically alter the results and render the measurement method inoperative. Moreover, the optical fiber sensors are always directed at one fixed area of the wafer. Since different parts of the wafer may have different device patterns and, therefore, may have different local emissivities, the temperature measurement and control would be limited in value as it would represent the emissivity information only for that specific area rather than the average surface topology of the substrate.
In addition to temperature uniformity, the uniformity of film deposition is affected by uniformity of the delivery of the process gas. Good process uniformity usually requires adjustments and optimizations for both the wafer temperature uniformity and the gas flow pattern of the process gas. In most conventional chambers or reactors, the reactant gas is delivered through a single port, which injects gas into the chamber above the wafer. Due to the geometry of the wafer, the resulting deposition of the gas onto the wafer is not uniform.
More recently, shower-like gas injection systems have been developed in which separate gases are injected in a shower-like pattern over the entire substrate area. However, such gas delivery systems fill the entire chamber volume and, thus, deposit films on the substrate as well as the chamber walls. Consequently, these gas delivery systems preclude the use of any optical instruments for non-contact temperature measurement and in-situ film methodology.
Consequently, there is a need for a processing reactor which can deliver heat to a substrate in a uniform manner and can accurately monitor the temperature of the substrate during processing and adjust the profile of the applied heat as needed to achieve optimal processing of the substrate. Furthermore, there is a need for a processing reactor which can deliver and direct the flow of gas to the substrate during processing so that the substrate receives a uniform deposition of thin film of the process gas or gases in a discrete area on the substrate.
One form of the invention provides a reactor having a processing chamber with an emissivity measuring device and improved gas injection system. The emissivity measuring device measures the photon density from a light source, which is housed in the processing chamber, and the reflected photon density off a substrate, which is processed in the processing chamber. These measurements are then used to determine the emissivity and, ultimately, the temperature of the substrate with a high degree of accuracy. The emissivity measuring device includes a communications cable which includes a photon or emissivity sensor that is positioned in the processing chamber. The photon density sensor is adapted to move between a first position wherein the photon density sensor is directed to the light source for measuring the incident photon density of the light and a second position wherein the photon density sensor is directed toward the substrate for measuring the reflected photon density off the substrate. The gas injection system is adapted to inject and direct at least one gas onto a discrete area of the substrate. The reactor is, therefore, particularly suitable for use in a semiconductor fabrication environment where the control of heating and injection of gas must be maintained in order to produce uniform process variables during the fabrication of semiconductor devices.
In one aspect, the emissivity measuring device comprises first and second communication cables. The first communication cable includes the photon density sensor and is in communication with the second cable for sending signals from the photon density sensor to a processor. Preferably, the first and second communication cables comprise optical communication cables. For example, the first communication cable may comprise a sapphire optical communication cable, and the second communication cable may comprise a quartz optical communication cable. In further aspects, the first and second communications cables are interconnected by a slip connection so that the first communication cable can be rotated between the first and second positions by a driver, for example a motor.
In another form of the invention, a reactor for processing a substrate includes a first housing, which defines a processing chamber and supports a light source. A second housing is rotatably supported in the first housing and is adapted to rotatably support the substrate in the processing chamber. A heater for heating the substrate is supported by the first housing and is enclosed in the second housing. A photon density sensor extends into the first housing for measuring the emissivity of the substrate, which is adapted to move between a first position wherein the photon density sensor is directed to the light source and a second position wherein the photon density sensor is positioned for directing toward the substrate. The reactor further includes a plurality of gas injectors, the gas injectors being grouped into at least two groups of gas injectors, with each group of gas injectors being adapted to inject at least one gas into the processing chamber of the reactor onto a discrete area of the substrate.
In one aspect, each group of injectors is adapted to selectively deliver at least one reactant gas and an inert gas. In another aspect, each group of gas injectors is adapted to be independently controlled whereby flow of gas through each group of gas injectors can be independently adjusted. In yet another aspect, the gas injectors in each group of gas injectors may be arranged in a uniform pattern for directing a uniform flow of a gas toward the substrate. The reactor also preferably includes an exhaust manifold for removing unreacted gas from the processing chamber.
In yet further aspects, the gas injectors are arranged in pattern having a greater concentration of gas injectors in a peripheral region and a smaller concentration of gas injectors in a central region of the substrate whereby the gas injected by the gas injectors produces a uniform deposition on the substrate.
In yet another form of the invention, a method of processing a semiconductor substrate includes supporting the substrate in a sealed processing chamber. The substrate is rotated and heated in the processing chamber in which at least one reactant gas is injected. A photon density sensor for measuring the emissivity of the substrate is positioned in the processing chamber and is first directed to a light, which is provided in the chamber, for measuring the incident photon density from the light and then repositioned to direct the photon density sensor to the substrate to measure the reflected photon density off the substrate. The incident photon density is compared to the reflected photon density to calculate the substrate temperature.
As will be understood, the reactor of the present invention provides numerous advantages over prior known reactors. The reactor provides a single substrate photon density sensor which can be used to accurately determine the temperature of the substrate during processing. The single photon density sensor eliminates the need for recalibration and complex calculations detailing the characteristics of each sensor associated with temperature measuring devices having two sensors. Moreover, the reactor provides a gas injection system which directs one or more reactant gases to the substrate during processing in a controlled manner and directs the gas or gases to discrete regions of the substrate so that emissivity measurements and temperature calculations can be performed in the processing chamber during the injection of the gas or gases without impairment from undesirable film depositions on the emissivity measurement devices.
These and other objects, advantages, purposes and features of the invention will be apparent to one skilled in the art from a study of the following description taken in conjunction with the drawings.